The invention relates to a tibia platform for an artificial knee joint comprising a metallic lower part which can be anchored in the tibia and a bearing part which is made of plastic, which has sliding surfaces for two femur condyles, which can be pivoted at the posterior at the lower part via an open hinge joint and which can be anchored at a distance "1" away from the hinge joint in the anterior direction at a projection of the lower part by a pawl.
A tibia platform of this kind is shown in the patent specification EP-A-0 738 504. In this design a pawl formed in a single piece on the bearing part latches under the projection of the lower part during assembly. Such bearing parts are often executed in plastic, for example in polyethylene, in order to achieve an advantageous sliding pairing with metallic femur condyles. The plastics used have the advantage that their structure and strength avoid high point loads. This means that limits are placed on these plastics when latching takes place using a pawl.
The direction and the maximum values of the forces that act on the bearing part and further on the lower part of the tibia platform depend strongly on how intact the ligamentary apparatus still is. The fewer ligaments that are still operative the more the femur condyles must be guided by a middle guide rib in the form of an artificial eminentia and the more extreme are the loads which act on the bearing part.